Electron multiplier tube having combined supporting-cooling means

ABSTRACT

A vacuum electron multiplier device is described having a cathode, one or more control grids, a plurality of dynodes, and an anode. The device is primarily designed for amplifying electrical pulses which are applied between the cathode and one of the control grids. All the dynodes, (except one) are made with a plurality of louvers for generating secondary electrons. All the electrodes are held in position by annular insulators which are mounted at a distance from the electron paths so as not to be under electron bombardment at any time. The dynodes and the anode are connected to air fin radiators having a heat-dissipating capability directly proportional to the average amount of heat generated by the associated dynode or anode.

United States Patent [7 21 Inventor Max Yarmovsky Livingston, NJ.

[21 Appl, No. 768,482

[22] Filed Oct. 17, 1968 [45] Patented Jan. 12, 1971 ['73] Assignee Wagner Electric Corporation a corporation of Delaware [54] ELECTRON MULTIPLIER TUBE HAVING COMBINED SUPPORTING-COOLING MEANS 11 Claims, 4 Drawing Figs.

[52] U.S.Cl 313/105, 313/l03,313/306 [51] Int. Cl ..1-101j 43/18, HOlj 43/22 [50] Field ofSearch 313/103, 104, 105, 301, 306, 307; 250/207 [56] References Cited UNITED STATES PATENTS 2,558,021 6/1951 Varian et a1. 313/103X Primary Examiner-Roy Lake Assistant Examiner-David OReilly Attorney-Eyre, Mann & Lucas ABSTRACT: A vacuum electron multiplier device is described having a cathode, one or more control grids, a plurality of dynodes, and an anode. The device is primarily designed for amplifying electrical pulses which are applied between the cathode and one of the control grids. All the dynodes, (except one) are made with a plurality of louvers for generating secondary electrons. All the electrodes are held in position by annular insulators which are mounted at a distance from the electron paths so as not to be under electron bombardment at any time. The dynodes and the anode are connected to air fin radiators having a heat-dissipating capability directly proportional to the average amount of heat generated by the associated dynode or anode.

ELECTRON MULTIPLIER TUBE HAVING COMBINED SUPPORTING-COOLING MEANS This invention relates to an electron multiplier device containing a plurality of coaxial dynodes in addition to the usual anode, cathode, and control electrodes. The invention has particular reference to a discharge device having dynodes which progressively increase in area as the electrical power increases. Each dynode is connected to a radiator fin for dis- I sipating the heat, the distance between the dynodes and the radiator cooling surfaces varying inversely as the amount of heat generated.

The present invention is an improvement over prior electron multiplier devices in that the heat generated bythe electrodes in the envelope is transferred to radiators in a highly efficient manner. Also, the insulator seals which separate the dynodes from each other are mounted in a position where sputtering from the electrodes cannot cause short circuits. The metal-to-insulator seals are under compression for greater dependability and the seals and components are arranged for easy fabrication and repair.

One of the features of the invention includes a plurality of dynodes whose length increases progressively as the current increases. This increase in length, coupled with the increase in diameter, results in a'progressive increase in dynode area which equalizes the current density to each dynode and provides greater power output with lower operating temperatures.

For a better understanding of the present invention, together with other details and features thereof, reference is made to the following description taken in connection with the accompanying drawings, of which:

FIG. 1 is a side view of one form of the invention with some parts shown in section;

FIG. 2 is a partial top view of the device drawn to a reduced scale and showing a portion of the envelope in section;

FIG. 3 is a cross-sectional view of the device shown in FIG. 1 and is taken along line 3-3 of that figure;

FIG. 4 is a schematic diagram of connections showing how the device may be used a a pulse amplifier.

Referring now to FIGS. 1, 2 and 3, the device includes an upper envelope portion which is, preferably made of KOVAR. On the inside cylindrical surface of this portion, a dynode 11 is mounted for rapid dissipation of heat and retained in position by means of an upper ring 12 which is brazed to the upper inside corner of the envelope before the assembly of the elements. The lower edge of dynode 11 is supported by a metal ring 19 which is welded to lip 10a extending downwardly from the lower end of envelope 10. An annular ring 70a is brazed to the bottom edge of upper envelope portion 10 to facilitate joining to the lower envelope portion described in subsequent paragraphs. The upper flat portion of envelope 10 is formed with a central hole and a copper tube 13 is brazed in the hole for the purpose of evacuation. The copper tipoff tube 13 is protected by a metal cap 14.

Inside the envelope and coaxially aligned with it is an electron emissive cathode which may comprise a hollow cylindrical tube 15 having a heater wire 16 to heat the tube to emission temperature. Around the outside surface of the cathode two control grids 17 and 18 are shown. The control portion of the discharge device may be a triode, a tetrode, or a pentode. The function of this section of the device is to send controlled beams of electrons to the dynodes and to the anode.

The control portion of the device is mounted on a composite stem which includes two mica spacers 20 and 21 and a plurality of coaxial hollow cylinders which may be inserted into another hollow cylinder 22. The cathode, heater, and the supporting rods which hold the grids are secured to other rods held by insulator disc 23. The insulator disc 23 may be joined to other similar discs for supporting the ends of the coaxial cylinders or the insulator discs may be formed integrally with steps as shown in FIG. 1 for properly spacing the cylinders. In the drawing, cylinder 24 is connected to the outer accelerating grid, cylinder 25 is connected to the control grid immediately adjacent the cathode I5, cylinder 26 is connected to the cathode 15 and one end of the heater wire 16, while the central wire 27 is connected to the other end of the heater. A set of insulator discs 28 supports the lower ends of the coaxial cylinders and retains them in their proper spatial relationship.

The first dynode 3G is spaced from the outer grid 17 and surrounds it. This dynode is secured to an insulator disc 31 at its upper end and is welded to a hollow cylinder 22 at its lower end. Supporting cylinder 22 is brazed to a metal base member 32 which is part of the envelope 10-. Dynode 36 has an axial length which extends for about the same distance as the cathode and the two grids. It is formed with a plurality of louvers, so positioned that electrons striking the louvered portions can generate secondary electrons which then pass to the second dynode 33. This second dynode 33 surrounds the first dynode 30 and is longer then first. Dynode 33 is secured to a metal ring 34 at its upper end and is welded to a hollow cylinder 35 at its lower end. Cylinder 35 is secured to a radial disc 36 which extends through the envelope and is connected to a sealing ring 37 on the outside of the envelope. Ring 37 forms a compression seal when brazed to its adjoining insulator rings 66 and 67 and is connected to a larger metal radiator ring 38 by radial fins 40. t

In a similar manner dynodes 41 and 42 are connected at their upper ends to metal rings 43 and 44 respectively and are welded to hollow cylinder 45 and '46 at their lower ends. Cylinders 45 and 46 are secured to discs 47 and 48 which are connected through the envelope to sealing rings 50 and 51. These sealing rings are respectively connected to radial fins 52 and 53 and to radiator rings 54 and 55 which are spaced from the envelope 10 for greater cooling efficiency.

It has been found convenient and more efficient to place the fifth dynode l1 adjoining the envelope wall 10 and to place the anode or collector 56 between the fourth and fifth dynodes. The fifth or outer dynode 11 may optionally have a knurled inner surface in order to increase the effective area of the surface upon which the electron beams impinge. In order to collect more electrons from both the fourth and fifth dynodes, the louvers in anode 56 are bent so that their surfaces are radial. This is best shown in FIG. 3. The anode 56 is connected to supporting cylinder 57 and annular radial disc 58. Disc 58 is connected to scaling ring'60 which forms a compression seal when brazed to insulator rings 61 and 62. Sealing ring 60 is connected to radiator ring 63 by radial fins 64.

The lower portion of the envelope is formed of five insulator rings 61, 62, 65, 66, and 67. These rings are preferably made of aluminum oxide but other ceramics may be used. Portions of the outside surfaces of the insulator rings are generally coated with a metal film and then, when the rings and discs are stacked together, the entire assembly is brazed together by heating in a hydrogen atmosphere.

The radiator fin assemblies shown in FIGS. 1 and 2 comprise a first metal sealing ring which fits closely against the outer surfaces of the insulator to form a compression seal. A second radiator ring is positioned a short did distance from the first ring, these two rings being joined by a plurality of radiator fins. This type or radiator assembly has been chosen because it forms an airtight seal with the two adjoining insulator rings, the spaces between the radial fins permit air to pass through the rings, and the outside radiator rings are in contact with circulating air currents. Radiator rings 55, 54, and 38 are formed similar to ring 63 except that they are made progressively smaller since they are required to dissipate decreasing quantities of heat. It should be noted that the first dynode 30 which is connected to a comparatively low voltage source generates the least amount of heat, this heat being conducted away from the dynode by means of the long cylinder 22 and the metal disc 32. The second dynode 33 generates more heat than the first dynode 36 and its path to radiator fin 38 is somewhat shorter. In like manner, the dynodes 4i and 42 generate increasingly larger amounts of heat and the paths of the heat to the radiator fins 54 and 55 is progressively shortened. The anode 56 has a short path through cylinder 57 and disc 58 to its first ring 60. Since the fifth dynode 11 is in contact with the KOVAR envelope ill) it needs no additional radiation means. it should be noted that, as the heat paths from the anode and dynodes become shorter, the effective cross section of the heat paths increases since the diameter of the associated cylinders increases. The thickness of the cylinders may also be progressively increased to further enhance the heat-dissipating capabilities of the heat paths. Thus, the thermal resistances of the heat paths associated with the anode with each dynode progressively decrease as the average heat generated by the anode of dynode with which each heat path is associated increases.

The upper portion of the upper insulator ring 611 is joined to the lower edge of the upper portion of envelope it) by means of an annular ring 'lilb which is formed to nest to the shape of ring 70a. Ring 70b is brazed to the upper edge of insulator ring 61. When the device is assembled, the upper portion, including the fifth dynode ill, the envelope i and ring 70a, may be placed over the assembly of dynodes and anode and the two joined together by welding the outermost edges of the two discs 79a and 70b. This is not only a convenient method of as sembly, it also provides a means for separating the two parts of the device for inspection and repair.

The lower insulator ring 67 is brazed directly to a metal ring 71 by first coating the insulator with a metal film and then brazing to form a compression seal. The lower edge of ring 71 is then are welded to the outer edge of base disc 32. in a similar manner the cathode-control unit is fabricated separately and then inserted into hollow cylinder 22. .The lower portion of the outer stem cylinder is then brazed to disc 32, thus forming a bead 72. This construction also permits the removal of the cathode-tetrode stem assembly at a later date for repair and for the installation of a new control unit.

As illustrated in FIG. 1, all the insulator rings 61, 62, 65, 66, and 67 are positioned at a distance from the source and path of the electrons. The path of an electron from the cathode or from any of the dynodes to an insulator involves an axial movement between the supporting cylinders and then a radial movement between discs. Because of this construction, the insulators are not subjected to any electron bombardment and metallic sputtering on the insulator surfaces is avoided.

The schematic circuit diagram shown in H0. 4* is one example of circuitry which may be used with this device. The cathode i5 employs an internal heater 16 to raise the cathode to an electron-emissive temperature. A control grid 18 is connected to one input terminal 75 in series with a blocking capacitor 76. The other input terminal '77 is connected to the cathode. When used as a pulse amplifier, the discharge device is generally biased for zero anode current at no input and to provide this bias, a battery 73 or other source of DC potential is connected between the cathode l5 and the control grid iii in series with a resistor Edi. Accelerating grids 17 may be optionally utilized.

The dynodes 3t 33, 4i, and 42 are each connected to various points of a voltage divider 81 which is energized by a source of direct current power 82. The voltages indicated in 4 have been found by experiment to work well and to give a large ratio of amplification. A second source of direct current power 83 is connected between the fifth dynode ii is series with a load 84 and the anode 56.

The advantages of the present invention, as well as certain changes and modifications to the disclosed embodiment thereofi, will be readily apparent to those skilled in the art. it is the applicants intention to cover all those changes and modifications which could be made to the embodiment of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.

l claim:

1. An electron multiplier tube comprising:

1. a sealed envelope;

2. a cathode, at least one control grid, and an anode mounted within said sealed envelope;

3. a plurality of secondary emission dynodes surrounding said cathode, said dynodes progressively'increasing in axial length as their respective distances from said cathode increases and, excepting the dynode most remote from said cathode, each having louvers formed therein;

4. a plurality of mounting means each comprising a tubular member connected at one end to anassociated dynode or anode, a radial member extending substantially radially from the other end of said tubular member, and a sealing ring extending substantially perpendicularly from said radial member external to said sealed envelope and forming an airtight seal therewith; and

5. a plurality of electrical connecting means operative to enable electrical connection from said cathode, said anode, and said at least one control grid and said dynodes to associated external circuitry.

2. The electron multiplier device according to claim 1 wherein said plurality of secondary emission dynodes and said anode are substantially cylindrical and coaxially mounted within said sealed envelope.

3. The electron multiplier device according to claim ll wherein each of said mounting means further includes cooling fins extending from said sealing ring.

4. The electron multiplier device according to claim 1 wherein said sealed envelope comprises a plurality of insulating ring members remote from said dynodes and said anode, said insulating ring members being separated from one another by said radial members of said mounting means.

5. The electron multiplier device according to claim ll wherein said electrical connecting means comprises a plurality of coaxial conductors and a plurality of insulating members spacing said coaxial conductors relative to one another.

6. The electron multiplier device according to claim 5 wherein said cathode and said at least one control grid are mounted between spaced insulating members and are each mechanically and electrically connected to an associated coaxial conductor by connecting members so as to form a removable control subassembly.

7. The electron multiplier device according to claim 1 wherein said anode is disposed between the two dynodes which are most remote from said cathode.

8. The electron multiplier device according to claim 7 wherein the louvers in said anode are disposed perpendicularly with respect to said anode.

9. The electron discharge device according to claim 1 wherein said sealed envelope comprises a metal upper portion, the dynode most remote from said cathode being mounted in contact with the inner surface of said metal upper portion.

it). The electron discharge device according to claim ll wherein the dynode most remote from said cathode is knurled.

ii. The electron discharge device of claim ll wherein said sealed envelope comprises:

1. a metal upper portion including a first flanged sealing ring;

2. a lower portion including a plurality of insulating rings separated by and attached to aid plurality of mounting means, and further including a second flanged sealing ring attached to the uppermost insulating ring, said first and se ond flanged sealing rings being attached to one another in a nesting relationship. 

1. An electron multiplier tube comprising:
 1. a sealed envelope;
 2. a cathode, at least one control grid, and an anode mounted within said sealed envelope;
 3. a plurality of secondary emission dynodes surrounding said cathode, said dynodes progressively increasing in axial length as their respective distances from said cathode increases and, excepting the dynode most remote from said cathode, each having louvers formed therein;
 4. a plurality of mounting means each comprising a tubular member connected at one end to an associated dynode or anode, a radial member extending substantially radially from the other end of said tubular member, and a sealing ring extending substantially perpendicularly from said radial member external to said sealed envelope and forming an airtight seal therewith; and
 5. a plurality of electrical connecting means operative to enable electrical connection from said cathode, said anode, and said at least one control grid and said dynodes to associated external circuitry.
 2. a cathode, at least one control grid, and an anode mounted within said sealed envelope;
 2. a lower portion including a plurality of insulating rings separated by and attached to aid plurality of mounting means, and further including a second flanged sealing ring attached to the uppermost insulating ring, said first and second flanged sealing rings being attached to one another in a nesting relationship.
 2. The electron multiplier device according to claim 1 wherein said plurality of secondary emission dynodes and said anode are substantially cylindrical and coaxially mounted within said sealed envelope.
 3. The electron multiplier device according to claim 1 wherein each of said mounting means further includes cooling fins extending from said sealing ring.
 3. a plurality of secondary emission dynodes surrounding said cathode, said dynodes progressively increasing in axial length as their respective distances from said cathode increases and, excepting the dynode most remote from said cathode, each having louvers formed therein;
 4. a plurality of mounting means each comprising a tubular member connected at one end to an associated dynode or anode, a radial member extending substantially radially from the other end of said tubular member, and a sealing ring extending substantially perpendicularly from said radial member external to said sealed envelope and forming an airtight seal therewith; and
 4. The electron multiplier device according to claim 1 wherein said sealed envelope comprises a plurality of insulating ring members remote from said dynodes and said anode, said insulating ring members being separated from one another by said radial members of said mounting means.
 5. The electron multiplier device according to claim 1 wherein said electrical connecting means comprises a plurality of coaxial conductors and a plurality of insulating members spacing said coaxial conductors relative to one another.
 5. a plurality of electrical connecting means operative to enable electrical connection from said cathode, said anode, and said at least one control grid and said dynodes to associated external circuitry.
 6. The electron multiplier device according to claim 5 wherein said cathode and said at least one control grid are mounted between spaced insulating memberS and are each mechanically and electrically connected to an associated coaxial conductor by connecting members so as to form a removable control subassembly.
 7. The electron multiplier device according to claim 1 wherein said anode is disposed between the two dynodes which are most remote from said cathode.
 8. The electron multiplier device according to claim 7 wherein the louvers in said anode are disposed perpendicularly with respect to said anode.
 9. The electron discharge device according to claim 1 wherein said sealed envelope comprises a metal upper portion, the dynode most remote from said cathode being mounted in contact with the inner surface of said metal upper portion.
 10. The electron discharge device according to claim 1 wherein the dynode most remote from said cathode is knurled.
 11. The electron discharge device of claim 1 wherein said sealed envelope comprises: 